1. Field of the Invention
The invention relates generally to uncooled infrared sensors, and in particular, the invention relates to various features and applications of an infrared uncooled sensor.
2. Discussion of the Related Art
A radiation detector is a device that produces an output signal which is a function of an amount of radiation that is incident upon an active region of the radiation detector. Infrared detectors are those radiation detectors which are sensitive to radiation in the infrared region of the electromagnetic spectrum. An infrared detector may be, for example, a thermal detector. A thermal detector detects radiation based upon a change in the temperature of an active region of the detector due to absorption of the radiation to be detected.
Thermal imaging sensors having a plurality of thermal detectors that detect a representation of an object by the objects' thermal emissions. In particular, energy emitted by an object is dependent on numerous quantities such as, for example, the emissitivity and the temperature of the object. Infrared thermal sensors typically detect one or both of these quantities and use the detected information to produce an image capable of being visualized by a user of the sensor.
Infrared detectors may be classified as, for example, either cryogenic (typically liquid nitrogen temperatures) or uncooled detectors. Cryogenic infrared detectors are typically made of small band gap (about 0.1-0.2 eV) semiconductors such as HgCdTe and operate as photo diodes or photo-capacitors by photon absorption to produce electron-hole pairs. In contrast, uncooled infrared detectors do not make use of the small band gap semiconductor device because the band gap is too small at, for example, room temperature such that any signal swamps the detector. Consequently uncooled infrared detectors may be less sensitive than cryogenic detectors but do not require a cooling apparatus or its associated energy consumption. For portable, low-power applications where the sensitivity of cryogenic detectors is not needed, the preferred choice is an uncooled thermal detector. A thermal detector may be any of three types typically: a pyroelectric detector, a thermocouple or a bolometer.
An array of bolometer detector devices may be formed integrally with an integrated circuit. The integrated circuit may be used to process electrical signals produced by the array of bolometers in response to the infrared energy impinging on the array of bolometers. In such an array, each of the bolometers includes an infrared energy receiving surface which is made of a material that has its resistivity change as its temperature changes, in response to the infrared energy impinging on and being absorbed by the material. Thus as the bolometer absorbs radiation, both its temperature and electrical resistance change. A measure of radiation absorbed by a bolometer can be made by measuring changes in its electrical resistance. For example, by placing the bolometer in series with a voltage supply, the current in the bolometer will vary in accordance with the infrared energy sensed by the bolometer. An electronic read-out circuit connected to the voltage supply and serially connected to the bolometer may be used to produce an output signal representative of the infrared energy impinging on the material. An array of such bolometers will produce a plurality of output electrical signals that may be fed to a processor and used to provide the electronic image of the source of the infrared energy.
Such infrared sensors have numerous applications such as missile guidance, thermal imaging, target acquisition, target tracking and law enforcement surveillance. Several prior art references disclose infrared imaging systems, methods, and arrays that make up such infrared sensors. The present invention is an improvement to an uncooled infrared imaging sensor.